Sorption cooling processes typically employ an adsorbent disposed in a metal vessel contained on a metal screen or surface which provides support for the adsorbent and permits the adsorbent to be placed in contact with a fluid stream containing an adsorbable component over the range of conditions necessary for adsorption and desorption.
In operation of sorption cooling systems, one or more solid beds containing a solid adsorbent are provided. The solid adsorbent beds desorb refrigerant when heated and adsorb refrigerant vapor when cooled. In this manner, the beds can be used to drive refrigerant around a heat pump system to heat or cool another fluid such as a process stream or to provide space heating or cooling. If two or more beds are used, the process may be continuous as at least one of the beds is heated to desorb refrigerant while another is cooled as it adsorbs the refrigerant. If a single bed is used, the desorbed refrigerant must be stored in a receiver before later being readsorbed later by the same bed.
In a single bed configuration, refrigerant is desorbed from the bed as it is heated to drive the refrigerant out, and the refrigerant vapor is conveyed to a condenser where it is cooled and condensed to a liquid. The liquid is stored in a receiver until it is needed for the adsorption process.
In some systems, the adsorption/desorption process requires that there be a difference between the actual vapor pressure of the refrigerant and the equilibrium vapor pressure of the refrigerant/sorbent compound. The adsorption/desorption process may be rate-limited by two transfer processes. First, the refrigerant must be able to freely move from the adsorber headers to the sorbent molecules. Second, the heat of adsorption/desorption must be quickly removed from the sorbent. If during adsorption, for example, the heat is not removed the sorbent heats and the equilibrium refrigerant vapor pressure is raised, thus stopping or reducing the adsorption process.
Further, the solid sorbent expands during adsorption and shrinks during desorption. This prevents tight packing of the sorbent into the bed, and may result in void formation between the sorbent and metal heat exchanger. One resistance to heat transfer is contact of the sorbent to the heat exchanger fins.